This invention relates to boiling cooling apparatus for cooling a heat generating member by utilizing the latent heat of vaporization of a boiling refrigerant, and more particularly to an open-type boiling cooling apparatus in which a cooling operation is performed at the atmospheric pressure.
A boiling cooling apparatus of the prior art essentially comprises an evaporator and a condenser which are enclosed in a sealed cooling vessel. The internal pressure of the cooling vessel may vary depending on the temperature of the refrigerant, and the temperature of the refrigerant varies greatly if there is a change in the ambient temperature or the amount of heat generated by the heat generating member. When, for example, C.sub.2 Cl.sub.3 F.sub.3 (Freon R-113) which is one of halogenated hydrocarbons is used as a refrigerant, the internal pressure of the cooling vessel varies from 0.15 kg/cm.sup.2 to 4.5 kg/cm.sup.2 (absolute pressure) when the temperature of the refrigerant changes from 0.degree. to 100.degree. C. Under such conditions, if the cooling vessel is not sealed airtight, a non-condensable gas, such as air, will invade the cooling vessel and greatly lower the performance of the condenser, in the event that the internal pressure is lower than the atmospheric pressure (1.033 kg/cm.sup.2 in absolute pressure). This will make it impossible for the cooling vessel to achieve the desired cooling effect, thereby causing inordinate overheating of or damage to the heat generating member. In case the internal pressure of the cooling vessel is higher than the atmospheric pressure, the refrigerant will be wasted by escaping from the cooling vessel to outside. This will also make it impossible for the cooling vessel to effect cooling satisfactorily. Thus the same result will be achieved when the internal pressure is higher than the atmospheric pressure as when the internal pressure is lower than the atmospheric pressure.
An important problem encountered when prior art apparatus are used is how to keep the cooling vessel airtight. Although the cooling vessel is constructed by welding together its parts, it is no easy matter to provide a completely airtight seal to the cooling vessel even if up-to-date techniques are utilized. Particularly, it is almost impossible to provide an airtight seal to a cooling vessel of a large size. When a refrigerant is charged into a cooling vessel, it is necessary to discharge all the non-condensable gas from the cooling vessel and the refrigerant. If this is not done satisfactorily, it will be impossible to obtain predetermined performance of the condenser, as it happens when no completely airtight seal is provided. To open the cooling vessel, it has hitherto been necessary to break open the welded joints. Thus difficulty has been experienced in effecting maintenance of the heat generating member.
The problem of how to provide an airtight seal to a cooling vessel could be solved if the apparatus were kept at the atmospheric pressure at all times. Stated differently, if the interior of the apparatus is kept at the atmospheric pressure, there will be no difference in pressure between the inside and the outside of the apparatus, thereby putting an end to mutual interference.
One problem encountered in keeping the interior of the apparatus at the atmospheric pressure is that the apparatus itself may become complex in construction and large in size. There is a dilemma as to whether an apparatus can be maintained at the atmospheric pressure without having air in the interior thereof.
For reasons stated above, it has hitherto been impossible to provide boiling cooling apparatus in which the problem of airtightness is solved and which has satisfactory cooling capabilities.